How many unsolved cases/outstanding warrants are there for voter fraud?

I have been debating with my friends for a while about the significance of voter fraud. In my state, there have been three people convicted of it over the past 40 years, and there are no cases in Maine of voter fraud fugitives.
In total in the US, how many outstanding warrants are there for voter fraud charges? Are there still any ongoing investigations of elections where it may have happened?